12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaEN 13941 regulation for single pipes and the calculatedvalues from the numerical simulations for parallelburied pipes is rather small. The values for the parallelburied pipes are slightly larger.CONCLUSIONThe earth pressure on district heating pipes is animportant design value and should be determined asexactly as possible. In the presented work the earthpressure on parallel buried pipes was investigated.The evaluation of the radial stresses on the pipe innumerical calculations showed a stress concentrationbetween two pipes buried in the same trench for shortpipe distances and large diameters. However, formertheoretical investigations led to a reduction of radialcontact pressure between the two pipes, which wasobserved in the numerical simulations for smalldiameters and small overburden heights.Because typical trench conditions with two parallelburied pipes are not considered in current designdirectives for district heating pipes the numerical resultswere compared with the values derived from thecurrent design regulations. For the observed systemsonly small deviations regarding the average normalpressure between single pipe and parallel buried pipeswere found. Thus, as long as the exact distribution ofstresses along the pipe perimeter is not of particularrelevance, current calculation directives are alsosuitable for parallel buried pipes. Only for conditionswith large pipe diameters and small distances betweenthe pipes and also relatively large overburden heightsis a significant deviation to be expected.Furthermore, inhomogeneous backfill compaction,which is probable for small pipe distances under in situconditions, affects the contact pressure. In order totake into account the real compaction process withinthe trench, only direct measurements seem to lead tocorrect results. Further research work is necessary atthis point.REFERENCES[1] DIN EN 13941, Berechnung und Verlegung vonwerkmäßig gedämmten Verbundmantelrohren fürFernwärme, Deutsches Institut für Normung e.V.,Beuth Verlag Berlin, 2003.[2] R Floss, „Handbuch ZTVE-StB 94/1997―,Kommentar mit Kompendium Erd- und Felsbau, 3.Auflage, Kirschbaum-Verlag, 2006.[3] ]G. Leonhardt, „Belastung von starrenRohrleitungen unter Dämmen―, PhD Thesis,Institute of Soil Mechanics, FoundationEngineering and Waterpower Engineering,University of Hannover, 1973.[4] ATV A 127, Richtlinie für die statische Berechnungvon Entwässerungskanälen und -leitungen,Arbeitsblatt A 127 der AbwassertechnischenVereinigung e.V., 2000.[5] O. Beilke, „Interaktionsverhalten des Bauwerks„Fernwärmeleitung–Baugrund―, Institute of SoilMechanics, Foundation Engineering andWaterpower Engineering, University of Hannover,1993.[6] V. Rizkallah, M. Achmus, ―Zur Größe derReibungskräfte an erdverlegten Fernwärmeleitungen‖,Forschungsvorhaben WechselwirkungenFernwärmeleitung – Bettungsmaterial, Institute ofSoil Mechanics, Foundation Engineering andWaterpower Engineering, University of Hannover,1993.[7] K. Hornung, D. Kittel, „Statik erdüberdeckterRohre―, Bauverlag GmbH Wiesbaden und Berlin,ISBN 3-7625-2039-9, 1983.In order to avoid large deviations in the contactpressures, good and consistent backfill compaction anda certain minimum distance between the flows andreturn pipes is recommended.15